Extreme cold temperature environments create problems for the use of electronic devices mounted on printed wiring boards (PWBs) or other multilayer interconnecting substrates, since devices may not have been designed to operate at the temperatures encountered (e.g., the minimum design temperature is higher). One exemplary application having exposure to such extreme environments is avionics circuitry. The risks posed to electronic devices operating in extreme cold weather environments include long and unpredictable warm-up time from turn-on until a system is functional, the possibility of failure to properly initialize (e.g., never reaching a point of functioning), and the risk of permanent damage to devices.
To address the risks posed by extreme cold environments, manufacturers and circuit designers have typically resorted to three approaches. The first is to restrict the use of devices to those which have been explicitly designed for the low temperatures to be experienced. This undesirably limits the available devices which could be used in the system.
A second approach is to screen devices which have not been designed for extreme cold temperatures. This entails testing individual devices at cold temperature, and rejecting those which fail to meet all functional and parametric requirements. Screening IC devices for cold temperature operation may typically increase cost by three to five times. Also, there is an ongoing risk that future production devices will fail screening and thus be unavailable for use, since there is no assurance by design that the parts work cold. Thus, the ability to use unscreened ICs in extreme temperature environments would be advantageous.
A third approach is to use unscreened electronic components, and to power-up the devices and rely on their power dissipation to warm-up the circuit until it is functional. The disadvantages are that the necessary warm-up time is long (since forcing all devices to dissipate maximum power during this period is difficult or impossible), and the warm up time is unknown, since power dissipation is unknown, because the parts may not be properly functioning. Finally, there is risk of unforseen failure during warm-up, such as failure to initialize, or actual circuit damage.
It would therefore be an advance in the art to provide a technique for preheating the electronic devices on PWBs or other interconnecting substrates prior to application of power to these electronic devices.